1. Field of the Invention
This invention relates to additives for improving lubricating characteristics of lubricating oils and more particularly, to lubrication boosting additives which, when added to lubricating oils for use in power engines, can improve load bearing properties of the oils and can prevent wear of the power engines while mitigating the lowering of an energy efficiency owing to the friction.
2. Description of the Prior Art
As is well known in the art, lubrication boosting additives have been widely used in order to improve lubricating characteristics of lubricating oils. Typical examples of the commercially sold additives include suspensions of polytetrafluoroethylene (PTFE) and molybdenum sulfide in the form of fine powder. Polytetrafluoroethylene is a resin which has good lubricating characteristics and a high chemical resistance, but is inconveniently insoluble in almost all the types of solvents, thus making it impossible to use the PTFE resin as a solution. This is why the PTFE resin is used as a fine powder suspended in a medium. However, the use of the suspension presents a serious problem with respect to its compatibility with or dispersability in lubricating oil. For instance, the fine powder may settle in the suspension prior to use or after mixing with lubricating oil. Alternatively, the fine powder may deposit in power engines or may clog filters used in association with the engines.
Moreover, the fine powder of PTFE or molybdenum disulfide rarely contributes to the improvement of the load bearing properties when added to lubricating oils.
We have already proposed in U.S. Pat. No. 4,826,614 a oil boosting additive which comprises a fluororesin and a phthalic ester dissolved in an organic solvent. This is very effective for use as an additive to lubricating oils which are employed in power engines. In this additive, the fluororesin is used in large amounts and is relatively expensive.